The high frequency of recessive lethals on a segment of the 2nd chromosome with high inversion frequency challenged a previously suggested role of chromosome inversions in maintaining sets of coadapted genes in natural populations of Drosophila albomicans. A hypothesis to account for the high frequency of both recessive lethals and the inversion heterozygosity is then proposed. After an investigation of natural populations from Wulai and Kuantzuling, Taiwan, it was found that In(2L)B1D5 heterozygosity reached 0.46 and the recessive lethal frequency related to it reached 0.44. The estimated recessive lethal frequency within this inversion region was 0.37. Since (2L)B1D5 in D. albomicans comprises only a quarter of the 2nd chromosome, the lethal frequency in this chromosomal segment of D. albomicans is indeed much higher compared to other Drosophila species. The coexistence of high lethality and high inversion heterozygosity is in accordance with our prediction of the trapping effect of inversions for recessive deleterious alleles. The accumulation of recessive lethals causes an increase of inversion heterozygosity, and the genetic load due to the principle of segregation seems to be the real reason for inversion heterosis.
Chromosomal inversion, Esterases, Lethality, Population genetics
